The present invention relates to apparatus for heating a railroad switch to prevent obstruction of the switch operation by ice or snow in cold weather conditions. In climatic regions that frequently experience temperatures below freezing, malfunction of railroad track switches is often a problem. This difficulty is compounded by frequent precipitation in the form of snow or freezing rain. Temperatures below freezing and accumulations of snow or ice may result in malfunction of railroad switches.
The heating of a railroad rail switch to prevent failure or unreliability of the switch operation under cold weather conditions involves a variety of problems and needs. The heating apparatus to be employed must serve reliably to keep the switch clear of ice and snow, with safety and efficiency in its operation, economy in the production and installation of its component parts, and assurance that failures of operation due to short-circuiting for example will not occur over long periods of service. It is also important that the apparatus be susceptible to safe installation by railroad workmen, to prompt repair at the switch location in the event of damage by accident or otherwise, and to fast removal and replacement whenever needed to enable repair or replacement of the rails, ties, or other structures at the switch.
These problems and needs have been satisfactorily met by the railroad switch heating system disclosed in U.S. Pat. Nos. Re. 31,081 and 4,388,523. These patents disclose an electrical resistance heating wire enclosed inside a substantially coextensive length of water-impervious, bendable tubing. The heating wire is provided on each of its ends with connectors for connecting it in a circuit containing other heating wires and a source of current for electrifying the heating wires such that they produce heat.
A length of such heating cable is disposed against a fixed rail adjacent to displaceable rail end portions of the railroad switch, in heat conducting relation thereto. High temperature resistant thermal insulation is held against the cable by channel members to prevent heat losses by convection and radiation. The heating of the fixed rails by conduction from the cable lengths results in conduction of heat to other parts of the switch.
The heating system also includes crib heating units fitting into crib spaces of the track, beneath tie rods of the switch. Each crib unit comprises a unitary elongate, substantially flat pan-like support of thermally conductive, heat and weather resistant sheet material, such as stainless steel or aluminum sheeting. The support is dimensioned to fit between and along the track ties bordering the crib space. A sinuously bent length of the electrical heating cable is arranged over and held to a surface of the pan-like support so as to heat the support substantially uniformly by conduction and thus heat substantially the entire region of the crib space by convection and radiation.
A connector according to the present invention is particularly useful, for example, for joining an end of the electrical resistance heating wire enclosed within the protective tubing with an insulated electrical conductor so that the connector not only makes an efficient electrical connection between the wires but, in addition, prevents harmful conduction of heat from the heating wire to the insulated conductor, enables quick disconnection or reconnection of the insulated conductor, and enables the joint to be made water-tight to avoid hazards of a short circuit. The connector should preferably also absorb thermal contractions and expansions caused by the cooling and the heating of the heating wire.
U.S. Pat. No. 4,391,425 discloses a connector including a heat-absorbing, electrically conductive core member that receives and is clamped onto an end of the core wire of the heating cable and an end of a wire of the insulated conductor. The core member is enclosed in electrically insulating material confined inside a rigid protective sleeve. A length of rigid smooth tubing encloses the heating cable and is joined in a water-tight manner to an end of the protective sleeve with a compression coupling. The insulated conductor is also joined in a water-tight manner to an opposite end of the protective sleeve with a compression coupling.
Thus, a water-tight connector exists that electrically joins a heating cable to an insulated conductor, yet absorbs and dissipates heat from the heating cable so as to prevent excessive heating of the insulated conductor. The connector also accommodates the thermal expansions and contractions that occurred with heating and cooling of the heating cable, and provides protection from water leakage.
What is desired, however, is a connector for joining an electrical heating cable with an insulated conductor that provides increased thermal expansion relief. What is also desired is an electrical heating cable having a protective tubing that provides increased heat conductivity.